(1) Field of the Invention
The present invention relates to a catalyst body containing in a carrier an alkali metal and/or alkaline earth metal, particularly Li, Na, K or Ca, which is used, for example, as an NOx adsorption catalyst for purification of automobile exhaust gas.
(2) Description of Related Art
In recent years, as the regulation for automobile exhaust gas has become severer, lean burn engines and direct injection engines have come to be used widely. Thus, in accordance with this change, NOx adsorption catalysts capable of effectively purifying the NOx present in an automobile exhaust gas under lean burn conditions have been put into practical use. As the NOx adsorption components used in the NOx adsorption catalysts, there are known alkali metals such as K, Na, Li, Cs and the like; alkaline earth metals such as Ba, Ca and the like; rare earth elements such as La, Y and the like; and so forth. Ba, in particular, has been widely used from the start of practical application of the NOx adsorption catalysts. Lately, addition of K superior in NOx adsorption ability at high temperatures has come to be tried.
An NOx adsorption catalyst is ordinarily constituted by (a) a carrier made of an oxide type ceramic material such as cordierite, or a metal material such as Fe—Cr—Al alloy and (b) a catalyst layer containing the above-mentioned NOx adsorption component, loaded on the carrier (a). The carrier, however, is easily corroded and deteriorated by alkali metals or some alkaline earth metals being activated under high temperature conditions derived from automobile exhaust gas, especially, Li, Na, K and Ca. In particular, there is a serious problem that a cordierite carrier made of an oxide type ceramic material generates cracks, since the carrier easily reacts with the above-mentioned alkali and alkaline earth metals, etc.